For crushing different products, a crushing technique is used in which the crushing bodies are long bars (80 mm in diameter and several meters in length), disposed substantially horizontally in a cylindrical crusher.
These crushing bars are used for fine or coarse crushing, dry or wet, and the products obtained may subsequently be treated in a ball mill.
Numerous products and processes have been tested as crushing bars, beginning with discarded laminated rails, simply cut to length and used as they are.
Crushing bars have been formed of materials rolled from a blank (ingot or billet), which orientates the fibers of the metal in the longitudinal direction, by hot deformation of the metal, under the pressure of a cylinder or a striking hammer. The fibers of the metal are normally orientated in the longitudinal direction of the bar (see for example U.S. Pat. No. 3 170 641).
In order to be easily rolled, the materials used to form the bars may be made from steel slightly alloyed with a carbon content less than or equal to 1.1% for, for example, an AISI 52100 or 1095 steel with more or less manganese.
The bars are rough rolled and straightened and, possibly, treated in accordance with processes which keep the bar straight (see, for example, U.S. Pat. No. 3,255,053). The treatment consists in austenization heating followed by cooling (quenching) so as to obtain a substantially martensitic structure from 50 to 60 RC. Bimetallic bars have also been used whose core is made from soft steel and whose surface is made from hard steel.
These materials can be rolled at a reasonable cost, and they are then alloyed with a limited carbon content. However, their wear rate is high, because of the limited amount of carbide.